I could do with a little help on the C of G positions on the following Fly Eagle Jet`s

F16 1/8th scale old version no honeycomb, balanced out at 150mm from leading edge at the moment.

F15 1/9th scale old version no honeycomb, balanced out at 200mm from leading edge at the moment.

I brought these second hand, so not flown them yet, all fitted out and ready to go, just need help with the best place to start with the C of G on these jets. I have searched other forums and I have read lots of information and many different CG positions,